Rigid frame motorcycles are those that do not include any suspension system for the rear wheel. The axle of the rear wheel is fixed to the frame and the frame does not allow any up and down movement. No form of suspension is provided to the rear wheel. Such frames are commonly described as “rigid” or “hard tail” frames. In contrast, “sprung” or “soft tail” motorcycle frames incorporate an axle mounting with some form of spring or shock absorber arrangement. For example, one or a pair of springs or shock absorbers may be connected to the frame at any angle to act directly on the axle, or to allow the axle to move via a swing arm that is connected to the frame. The spring or shock absorber is attached to the frame at one end and to the swing arm at the other end. The current standard swing arm arrangement is that the spring or a linkage on which the spring acts is attached to the swing arm at a point between the axle connection to the swing arm and the pivotal connection of the swing arm to the frame.
Swing arm type motorcycle rear suspension systems have the swing arm pivotally connected to the frame at a location close to the gearbox of the motorcycle and supported by springs or shock absorbers close to the rear axle. A more rigid version includes a triangulated swing arm pivoted close to the rear of the gear box and supported by one or two shock absorbers mounted either side of the seat of the motorcycle or under the gear box.
Another suspension system used before the advent of swing arm systems includes vertically mounted springs or shock absorbers located at both ends of the rear of the frame with the axle attached towards the middle of the spring unit.
Rigid frame motorcycles have a unique appearance by virtue of their generally low stance, low seat position, overall design simplicity and flowing lines. Design simplicity and low seat position is achieved by removing non-essential parts including the rear wheel suspension. Such frames are also light in weight and this is an important factor for most riders who choose to ride such motorcycles.
As a consequence of not including any suspension for the rear wheel, the ride of the motorcycle is poor in bumpy conditions and during cornering. Many older riders find riding such motorcycles uncomfortable. Control of the motorcycle, particularly when cornering is also an issue.
In order to make the ride of such motorcycles more comfortable, attempts have been made to provide suspension to the rear wheel whilst still maintaining the rigid frame appearance. Most of these attempts have not been very successful.
The present invention seeks to provide a suspension system for the rear wheel of a motorcycle that retains the general appearance of a rigid frame.
The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of this application.